These investigations have been exploring: 1) the place of the intestinal mucosal enzyme Na-K-ATPase in in vivo absorptive and secretory processes; 2) the mechanism by which the glucocorticoid methylprednisolone alters intestinal transport processes; 3) the mechanism by which serotonin stimulates intestinal secretion; and 4) the possible use of the B-receptor antagonist propranolol as an inhibitor of active and passive intestinal secretory processes.